A long throw-in fell for Mathias Jorgensen by the far post, and he squeezed his left-footed chance through traffic for the first worldwide goal of his career to cement a dream start for the Danes.
Croatia bounced back nearly immediately and in the 4th minuted leveled when Mandzukic finished off from a lucky rebound off a Danish defender.
Brathwaite clears, but the ball finds it's way to Modric again, with his shot deflected out for another corner.
Liverpool defender Lovren glanced Luka Modric's free-kick wide late in the first period, before the sides played out a keenly-contested - and goalless - second half. Rakitic went close just before the break but his left-footed shot from inside the box did not trouble Schmeichel.
Dalic introduced Mateo Kovacic for with twenty minutes remaining and Croatia started to lift the tempo again.
A Modric shot from outside the box was off target as the game entered its final 15 minutes, and Rebic fired in an optimistic strike that Schmeichel held.
Just as Croatia, Denmark have lost only two games this calendar year.
With the match 1-1 after extra time, spot kicks were needed for the second time in the day to decide a last-16 tie.
Both teams concidentally had their best World Cup showings 20 years ago.
106' - Second period of extra time begins. But Croatia have just enough artillery in their skill set to cross Denmark's hurdle but they might have to grind it out to achieve the desired result.
He also said he has studied the way Croatian players shoot penalties when playing with their teams, in case the match goes to a penalty shootout.
To view the Croatia vs. Denmark FIFA World Cup knockout stage match stream live for free without a cable subscription, fans may sign up for a free trial of an "over the top" streaming TV package such as Sling TV, YouTube TV, or DirecTV Now. Kramaric leveled at 1-1 before Modric made it 2-2. Subasic was the hero as he saved his third penalty leaving Ivan Rakitic to slot home the victor. We're going to penalty kicks. We deserved to win.
Schmeichel guessed right to thwart Pivaric with a diving stop, Jorgensen's penalty down the middle then blocked by Subasic after he had failed to fool the keeper with a stop-start run-up. We must be very careful.
"We have many good players, but we have a team which is what has taken us so far".